JPS5818619A - Exposure measuring apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exposure measuring device for a reflex camera in which an image of an object projected onto an image plane by a photographing objective lens can be observed by an eyepiece lens through a pentaprism.

For example, according to U.S. Pat. No. 3,612,705, in order to control the required exposure, it is necessary to select between, on the one hand, image plane parts that are representative of the entire image plane (so-called large field measurement) and, on the other hand, particularly important image planes of the image. It has become known to use only parts (so-called selective measurements) for measurements. The switching between these two measurements is hereby carried out by using an at least partially translucent reflector, which directs the light rays attached to the central area of the image plane into the first receiver. The light rays attached to the receiver and other areas are directed to a further receiver or receivers, the output signals of which can be switched individually or in combination in a suitable manner, i.e. electrically switched. Where possible, it is sent to the evaluation device.

Furthermore (for example, West German Patent Publication No. 2826947
It is known to direct light from the entire area or only from a partial area to a photoelectric receiver by optical means, for example using a switchable lens or a diaphragm.

However, the known arrangement as described above has the disadvantage that the brightness of the viewfinder image is reduced due to the splitting of the light stream via an at least partially translucent reflector.

SUMMARY OF THE INVENTION The object of the invention is to create an exposure measuring device in a reflex camera, in which the light stream passing through the photographing objective forms a bright viewfinder image and a photoelectric receiver without significantly reducing the brightness. It is something that can be stimulated.

The above purpose is to selectively perform full exposure measurement or partial exposure measurement on the lower edge of the light exit surface of the pentaprism, which allows the image of the object projected onto the image plane by the photographing objective lens to be observed by the eyepiece lens. A semi-transparent concave mirror is provided in order to perform the imaging, and the angle of the pentaprism is formed at such an angle that a portion of the light flow passing through the exit pupil of the imaging objective is incident on the concave mirror. The concave mirror and the surface of the prism located behind the concave mirror in the direction of propagation of the light beam are each provided with at least one photoelectric receiving system, the output signals of which are transmitted to the indicating device and/or
This is achieved by controlling the exposure control device.

In order to selectively perform total exposure measurement or partial exposure measurement, a semi-transparent concave mirror is installed at the lower edge of the light exit surface of the pentaprism, and a supplementary mirror is attached to the prism so that the path of the light rays inside the pentaprism is as desired. Adding optical components,
The element can also cooperate with a pentaprism in such a way that a portion of the light stream passing through the exit pupil of the recording objective reaches the concave mirror.

A characteristic formation of the device according to the invention is defined in claim 3.
It is described in items 6 to 6.

Embodiments of the invention are shown diagrammatically in the accompanying drawings.

FIG. 1 shows schematically the housing 1 of a 7-rex camera, which housing has a recording objective 2 as well as a reflector 3 in a known manner. Above the reflecting mirror 3, a focusing plate 4 is formed integrally with the field lens 5 in this figure.
exists. Through the reflecting mirror 3, the photographing objective lens 2
is an image B of an object (not shown) on the surface of the focusing plate 4.
' is projected, and the elementary image can be viewed by the camera or camera user through a pentaprism 6 that erects the image and an eyepiece 7 that functions as a magnifying glass. The brightness of this image is proportional to the light flow per unit area of the exit pupil AP of the objective lens 2. A real image of the exit pupil AP of the photographing objective described above is imaged as AP' in the vicinity of the eyepiece 7 by the filled lens 5, which can be formed as a Fresnel lens although it is not necessary to do so; The real image is significantly larger than the exit aperture of the eyepiece 7 due to the predetermined spatial arrangement.

The dimensions of the pentaprism 6 are such that, after the optical axis of the light path has changed direction twice at the reflecting surfaces 6a and 6b of the pentaprism 6, it is parallel to the optical axis of the photographing objective 2 toward the rear. It is designed to be ejected from the outer casing of a reflex camera. The eyepiece 7 is arranged so that its optical axis coincides with the optical axis of the emitted light path. A light path passes through a pentaprism 6 between a photographic objective lens 2 and an eyepiece 7.
The part that passes through is called the finder optical path. The optical path is designated in the figure by the symbol 8 and is indicated by a dash-dotted line.

A semitransparent concave mirror 16 is arranged at the lower edge of the exit surface attached to the eyepiece 7 of the pentaprism B.

By varying the angles of the surfaces 6a and 6b, the exit pupil image AP' is displaced in the direction of the concave mirror 16. The user's eye is impinged by a partial light stream coming from the upper region of the pupil of the photographing objective 2, while the concave mirror 16 is impinged by light coming from the lower half of the pupil of the objective 2. Due to the constant reflection of the incident light stream, a constant portion of the light stream, for example 50%, passes through the concave mirror 16 and stimulates one charging receiver system 9. This light flow fraction is proportional to the total light flow passing through the objective pupil.

The receiver system 9 therefore emits a signal proportional to the average value of the overall image brightness.

The light flow portion reflected by the concave mirror 16 projects an intermediate image AP' behind the prism surface 6c located behind the four-sided mirror 16 on the optical path, and the central portion 11 of the intermediate image is picked up by the diaphragm 10. .

The light flow through the aperture 10 is proportional to the average brightness of this central image area. This light stream is converted into an electrical signal by a second photoelectric receiver system 12 located behind.

The electrical signals from the two receiver systems 9 and 12 are alternately, selectively or combined in a suitable manner and sent to an indicating device and/or evaluation electronics for exposure control, not shown in detail. .

The displacement of the pupil can be such that the optical axis of the light path above the focusing plate 4 coincides with the separation line between the eyepiece 7 and the concave mirror 16.

As mentioned above, the displacement of the pupil is realized not only by appropriately deforming the pentaprism 6 (FIG. 2a), but also by arranging a wedge-shaped medium on the plane of the focusing plate 4. Ru.

FIG. 2b shows an additional wedge 13 for changing the direction of the light beam in accordance with the above, which wedge can also be formed as a stepped wedge grating 14a and 14b, as shown in detail in FIG. 2C. be.

Furthermore, such a wedge effect can also be brought about by appropriately forming the Fresnel lens 15 itself, which is not rotationally symmetrical, as shown in FIG. 2d.

It is also possible to shift it in the opposite direction. This is because a lens placed at an eccentric position has the same effect as a combination of a lens and a wedge.

However, such eccentricity deteriorates the imaging results when the amount of variation is large.

By suitable switching, the charging receiver system 12 can be used as a focus detector in a known manner.

Variations of the illustrated embodiment are also possible. That is, for example, aperture 10
can also be designed as a variable diaphragm. At least one of the receiver systems 9 or 12 can be represented by only one receiver.

It is also possible to provide the pentaprism 6 with one or more supplementary elements in order to achieve the desired path of the light beam.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a reflex camera equipped with the device of the invention, and FIGS. 2 and 2d are optical means 1 for realizing the lateral transition of the exit pupil of the photographic objective lens...Outer casing of the camera 2...Photography objective lens 6...Penta prism
6C...Face 7 of the pentaprism...Eyepiece
9, 12... Light receiver system 10... Aperture 13.14a, 14b, 15... Optical member 16...
Concave mirror AP...exit pupil.

Claims (1)

[Scope of Claims] 1) In an exposure measuring device for a reflex camera in which an image of an object projected onto an image plane by a photographing objective lens can be observed by an eyepiece lens through a pentaprism, a total exposure measurement device is used. Alternatively, in order to selectively perform partial exposure measurement, a semitransparent concave mirror (16) is provided at the lower edge of the light exit surface of the pentaprism (6), and the angle of the pentaprism (6) is The exit pupil of (2) (
The concave mirror (16) is formed at an angle such that a portion of the light flow passing through the concave mirror (16) is incident on the concave mirror (16);
16) and the surface (6C) of the prism located behind the concave mirror when viewed in the direction of propagation of the light beam, one photoelectric receiver system (9, 12) is attached to each, and these output signals are transmitted to the indicating device and (or) An exposure measuring device characterized by controlling an exposure control device. 2) Select full exposure measurement or partial exposure measurement in the exposure measurement device of a reflex camera that can be observed with the eyepiece via the object, image force, or hentabism projected onto the image plane by the photographic objective lens. In order to achieve this, a semitransparent concave mirror (16) is provided at the lower edge of the light exit surface of the pentaprism (6), and the prism is in addition to at least one additional optical component (1
3, 14a, 14b, 15) are provided, which optical components cooperate with the pentaprism (6) to direct a portion of the light stream passing through the exit pupil (AP) of the photographing objective (2). An exposure measuring device characterized in that the exposure measuring device is configured to reach a concave mirror (16). 3) The optical axis is a concave mirror (16) and a camera (1) eyepiece (
7) The exposure measuring device according to claim 1 or 2, characterized by a light beam guide that passes through a boundary line between the prism attached to the prism and the exit surface. 4) according to claims 1 to 6, characterized in that at least one of the photoelectric receiver systems (9, 12) is provided with a diaphragm (10) in front. The exposure measuring device according to any one of the above. 5) The exposure measuring device according to claim 4, wherein the aperture of the diaphragm (10) is variable. 6) Any one of claims 1 to 5, characterized in that it is used for determining the distance between the object to be imaged and the photographing objective (2). The exposure measuring device described in .